Electronically controlled bypass clutch based on percent-shift-completion for a torque converter

ABSTRACT

A multiple ratio automatic transmission having a hydrokinetic torque converter in an automotive vehicle driveline wherein the torque converter has a controllable bypass clutch and wherein provision is made for changing the clutch capacity during a ratio change to reduce undesirable torque fluctuations in the driveline, thus improving shift quality while maintaining optimum hydrodynamic torque converter efficiency.

TECHNICAL FIELD

This invention relates to automatic transmissions having a hydrokinetictorque converter with a bypass friction clutch and to an electroniccontroller for the bypass clutch.

BACKGROUND ART

The improvements of our invention may be applied to a hydrokinetictorque converter transmission of the kind disclosed, for example, inU.S. Pat. Nos. 4,978,328, 4,637,281, and 5,029,087, which are assignedto the assignee of this invention. Those references disclose afour-speed transaxle transmission for use in an automotive vehicledriveline. The transaxle has two simple planetary gear units arranged ona first axis transversely disposed with respect to the center plane ofthe vehicle and a torque transfer drive between torque output elementsof multiple ratio gear units to each of two traction wheels through halfshaft assemblies in a front wheel drive arrangement. The engine ismounted with its crankshaft arranged in spaced parallel relationshipwith respect to the axis of the planetary gearing. A hydrokinetic torqueconverter, mounted on the crankshaft axis, is connected by means of achain drive to torque input elements mounted on the planetary gearingaxis.

The torque converter of these prior art designs has a controllablebypass friction clutch that is engageable to establish a mechanicaltorque transfer between the crankshaft of the engine and the turbine ofthe converter, thus bypassing the hydrokinetic torque flow path.

The improvements of this invention can be applied also to a rear wheeldrive transmission of the kind shown for example in U.S. Pat. No.4,934,216. That transmission includes a hydrokinetic torque converterand multiple ratio gearing mounted on an axis that is common to theengine crankshaft axis. The torque converter of the design shown in the'216 patent also includes a friction bypass clutch.

It is desirable to control the capacity of the bypass clutch to effect acontrolled slip in the clutch to compensate for torque transients and toeliminate noise vibration and harshness in the driveline. U.S. Pat. No.5,029,087 describes one method for achieving a controlled slip in abypass clutch. The clutch of that reference establishes a controlledslip condition by relying on engine speed and turbine speed signals. Itcontinuously monitors the difference between the actual converter slipat any instant and a desired slip. That error is used to compute a dutycycle for a solenoid-operated pressure controller for the bypass clutch.The slip is controlled in this fashion until a final target slip isachieved. The target slip is a value stored in a microprocessor memory.Its magnitude depends upon throttle position and vehicle speed.

A microprocessor controller is used in a closed loop control circuit toestablish partial clutch engagement rather than a full mechanical torquebypass through the clutch during a major portion of the operating time.The bypass clutch will permit the converter to operate near 100%mechanical efficiency when the driveline is operating in a steady-statemode.

The microprocessor responds to converter slip which is computed bysensing the turbine shaft speed and the engine speed and determining anerror in the slip, the error being the difference between the actualslip and a desired slip. The desired slip depends upon information froma throttle position sensor, an engine speed sensor, a gear shiftselector sensor, an oil temperature sensor, a vehicle speed sensor, anda transmission input shaft speed sensor.

In related copending patent application Ser. No. 922,627, filed Aug. 10,1992, a modulated bypass clutch controller is described. That controllerwill achieve a controlled slip condition after the bypass clutch iscommanded by the transmission control system to engage. After asteady-state condition is achieved, the controller will effect aso-called desired slip that will equal the target value. After thetarget value is reached and steady-state conditions continue, thedesired slip may be reduced to zero or near zero to eliminatorsubstantially eliminate slip in the hydrokinetic unit, thereby providingan added improvement in overall transmission operating efficiency. Thisalso tends to improve durability of the clutch by providing moreefficient torque energy management as friction heat is reduced.

Application Ser. No. 926,627, Aug. 10, 1992, was filed by A. L. Leonard,Kenneth, Walega and David Garrett, John Daubenmier, Bruce Palansky,Thomas Greene and Lawrence Buch, and is entitled "Automatic TransmissionControl System". It is assigned to the assignee of the presentinvention. That application discloses a bypass clutch arrangement in amultiple ratio transmission wherein a close loop control of the bypassclutch capacity is effected by establishing a desired slip duringsteady-state operation following a command for clutch engagement. Thedesired slip is determined by setting it equal to the actual measuredslip and then ramping the desired slip to achieve a progressivelydecreasing converter slip until a target value is reached. Aftersteady-state operation is achieved and the desired slip is equal totarget slip, the controller will cause a transition from the open loopslip control into a so-called "hard lock" mode in which the desired slipis again ramped to provide progressively decreasing actual slip until azero slip or a near zero slip is effected. The near-zero slip conditionis sometimes referred to as a "soft lock" mode.

The transmission disclosed in the copending application identified abovedoes not include a turbine speed sensor, but it does include a vehiclespeed sensor. It thus is necessary for purposes of carrying out thebypass clutch control strategy to compute, during each backgroundcontrol loop of the microprocessor, a turbine speed using a currentvehicle speed value and a current gear ratio value for the transmissiongearing.

The control strategy for the bypass clutch control disclosed in thecopending application identified above makes provision for modulatingthe bypass clutch pressure during shift intervals. This is done to avoidundesirable torque transients during the shift. It is necessary in thedesign of the copending application to continuously monitor calculatedspeed ratio across the converter. When a predetermined delta speedratio, or speed ratio difference, is detected, that is an indication ofthe beginning of a shift following the command of a shift by the controlsystem processor. Pressure modulation occurs, following the detection ofthe beginning of the shift, through the shift interval and is ended whenthe processor detects that the so-called delta speed ratio issufficiently high to indicate that the shift actually has come close tocompletion. The processor then will return to the close loop control,and that in turn is followed by the so-called hard lock mode or softlock mode described above.

The clutch control of the present invention has features that are commonto the controller and the control strategy described in the copendingapplication. Those common features relate in general to the behavior ofthe bypass clutch following a command for clutch engagement and prior toa command for a change in speed ratio. Those common features relate alsoto the behavior of the clutch after the completion of a shift interval.The transmission of the present invention includes a turbine speedsensor, and in this respect it differs from the transmission describedin the copending application. Thus, the behavior of the clutch and thecontrol strategy for effecting control of the clutch during the shiftinterval differs from that described in the copending application.

BRIEF DESCRIPTION OF THE INVENTION

The clutch controller of the present invention functions to enable andto disable the clutch and to allow continuous modulation of the clutchduring definable regions of the clutch operating schedule. It controlstransitions between the open loop, initial engagement mode, the softlock mode, the shift interval operating mode and the hard lock mode.

Our improved control system is capable of controlling the clutch,particularly during shifting, to provide improved durability andimproved energy management throughout the entire operating range of theclutch. It does this by controlling torque transients during applicationand release of the clutch, particularly during shifts. The torquemanagement during a shift is achieved as a function of the percent ofshift completion following the command of the shift so that the dutycycle of the solenoid-operated clutch pressure control can be varied asa function of the percent of shift completion following the command ofshift and by providing a unique set of algorithms for controlling theclutch as a function of the progression of the shift between themodulation mode, the hard-lock mode and the shift-lock mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows in schematic form a multiple ratio transaxle having ahydrokinetic torque converter in an automotive vehicle driveline whereinthe torque converter has a bypass clutch that is controlled by theprocessor and control strategy of the present invention;

FIG. 2 is a chart that shows the clutch and the brake engagement andrelease pattern for the transmission schematically illustrated in FIG.1;

FIG. 3 is a schematic representation of the bypass clutch control valvecircuit which includes a turbine speed sensor, a microprocessor, abypass clutch solenoid valve, a bypass clutch control valve and thefluid circuits between the bypass clutch control valve and the bypassclutch for the converter;

FIGS. 4A and 4B in schematic form the control elements of the bypassclutch control including the microprocessor, the hydraulic valve bodyand the planetary gearing together with the various sensors that developsignals that are used by the processor to establish shift points in thetransmission itself as well as signals for the converter bypass control;

FIG. 5 shows the proportional-integral-derivative close loop controlsystem for the bypass clutch schematically illustrated in FIG. 3;

FIG. 6 is a schematic cross-section representation of a solenoidregulator valve for establishing a controlled bypass clutch pressure;

FIG. 7 is a chart that shows the shift points for the transmission as afunction of vehicle speed and throttle opening, each shift having anindependent shift point curve;

FIG. 8 shows the relationship between the target slip and desired slipvalues for the present transmission as a function of time measured onthe horizontal axis;

FIG. 9 is a chart that shows the time-based relationship between turbinespeed, engine speed and the calibration constant "percent shiftcomplete" during a shift interval following the command of a shift;

FIG. 10 is a chart showing the relationship between the percent of shiftcompletion and the target slip, which is a relationship that iscalibrated by the calibrator for the transmission control system andstored in the memory of the processor;

FIG. 11 is a control strategy flow chart that illustrates the processsteps and control functions that are executed by the processor during ashift interval; and

FIGS. 12 and 13 show the relationship of solenoid current and computervoltage output for the solenoid with respect to time.

PARTICULAR DESCRIPTION OF THE INVENTION

In FIG. 1, numeral 10 designates the crankshaft of an internalcombustion engine. Crankshaft 10 is connected to the impeller 14 of ahydrokinetic torque converter 16. The converter 16 includes also abladed turbine 18 and a bladed stator 20, the latter being locatedbetween the torus flow outlet section of the turbine 18 and the torusflow inlet section of the impeller 14. The stator 20 is supported by astationary sleeve shaft 22 connected to the transmission housing shownat 24 in FIG. 3. An overrunning brake 26 is situated between the bladedsection of the stator 20 and the stationary sleeve shaft 22. Overrunningbrake 26 permits freewheeling motion of the stator 20 in the directionof rotation of the impeller, but it prevents rotation in the oppositedirection.

A torque converter lockup clutch 28 is adapted to establish a drivingconnection between the impeller 14 and turbine shaft 30 (FIG. 3), thelatter being connected to the bladed impeller 18. For a completedescription of the mode of operation of the clutch 28, reference may bemade to the previously identified patents.

The engine crankshaft 10 is connected to a pump driveshaft 29, whichdrives a variable displacement pump 38 for the automatic transmissioncontrol system. Turbine shaft 30 (FIG. 3), which is a sleeve shaftsurrounding driveshaft 29, serves as a torque input shaft for a drivesprocket 32. A driven sprocket 34 is connected to torque input shaft 36for multiple ratio gearing disposed about the output shaft axis 38. Axis38 is parallel and laterally offset with respect to the enginecrankshaft. Drive chain 40 serves as a torque transfer member thatconnects drivably the drive sprocket 32 with the driven sprocket 34.

The multiple ratio gearing comprises a pair of simple planetary gearunits 42 and 44 as well as a final drive planetary gear unit 46. Gearunit 42 includes ring gear 48, sun gear 50, a planetary carrier 52 andmultiple planet pinions 54 which are journalled on carrier 52 so thatthey mesh with ring gear 48 and sun gear 50.

Carrier 52 is connected directly to ring gear 56 of the planetary gearunit 44. Gear unit 44 includes also sun gear 58, planetary carrier 60and planet pinions 62 journalled on carrier 60 so that they mesh withring gear 56 and sun gear 58.

Sun gear 58 is adapted to be braked by a low and intermediate brake band64 which surrounds brake drum 66 connected to the sun gear 58. The lowand intermediate brake 64 carries the notation B₂ in FIG. 1 as well asin the chart of FIG. 2.

A reverse brake 68 selectively brakes the ring gear 56 and the carrier52 which are connected together as explained. Brake 68 in FIG. 1 carriesthe notation CL₄ in FIG. 1 as well as in the chart of FIG. 2.

Carrier 60 is connected to torque output shaft 70 for the planetarygearing. Shaft 70 is connected to sun gear 72 of the final driveplanetary gear unit 46. Gear unit 46 includes also ring gear 74 which isheld stationary by the transmission housing. Gear unit 46 includes alsocarrier 76 which journals pinions 78 that mesh with ring gear 74 and sungear 72. Carrier 76 is connected to the differential carrier of adifferential gear unit 80. The differential carrier has pinions 82journalled thereon, and these are connected drivably to the carriers 76.

Differential gear unit 80 includes also side gears 84 and 86. Each sidegear is connected to a separate torque output half-driveshaft, theoutboard ends of the driveshafts being connected to the vehicle tractionwheels. A universal joint, not shown, connects one end of each halfshaft with its associated side gear and the outboard end of that halfshaft is connected to its associated traction wheel by a seconduniversal joint, not shown.

The input sleeve shaft 36 is connected to the carrier 52 of gear unit 42through an intermediate speed ratio clutch 88. That clutch is identifiedby the symbol CL₂ in FIG. 1 as well as in the chart of FIG. 2. Sun gear50 of the gear unit 42 is connected to brake drum 90 about which ispositioned overdrive brake band 92. Brake band 92 is identified by thesymbol B₁ in FIG. 1 as well as in the chart of FIG. 2. Sun gear 50 andbrake drum 90 to which it is connected is connected to input shaft 36through forward clutch 94 and overrunning clutch 96 situated in seriesrelationship. Clutch 94 is identified by the symbol CL₁ in FIG. 1 aswell as in the chart of FIG. 2. The overrunning clutch 96 is identifiedby the symbol OWC₁ in FIG. 1 as well as in the chart of FIG. 2.

A direct drive clutch 98 and a second overrunning clutch 100, which arearranged in series relationship, connect input shaft 36 with the brakedrum 90 and the sun gear 50. The symbol CL₃ identifies the direct driveclutch in FIG. 1 as well as in the chart of FIG. 2. A second overrunningclutch is identified by the symbol OWC₂ in FIG. 1 as well as in thechart of FIG. 2.

By engaging selectively the clutches and the brakes, four forwarddriving speed ratios can be achieved as well as a single reverse speedratio. The forward clutch 94 is engaged during operation in the firstthree forward driving ratios and the intermediate clutch 88 is engagedin the second, third and fourth forward driving ratios. Direct driveclutch 98 is engaged during operation in the third and fourth forwarddriving ratios as well as the reverse driving ratio. It is engaged alsoduring manual low operation to effect a bypass around the overrunningclutch 100 during engine braking.

Sun gear 50 acts as a reaction member during overdrive operation. It isbraked by overdrive brake band 92 which is applied during fourth ratiooperation. Low and intermediate brake band 64 is applied duringoperation in low and intermediate operation.

In the chart of FIG. 2, the clutch engagement and release pattern isindicated. A symbol "X" is used to define an engaged clutch or brake.The symbol O/R is used to indicate an overrunning condition for theappropriate overrunning clutch.

As shown in FIG. 3, a cavity within the impeller housing 120 is formedbetween the shroud 124 of the turbine and the end wall 122. A clutchplate and damper assembly 126 is disposed in that cavity.

Assembly 126 is splined to turbine hub 128, which in turn is splined toturbine sleeve shaft 30 extending through the hub of stator 20 and thehub of impeller 14.

When the clutch plate 132 is pressurized by the pressure in the toruscircuit, the friction surface 134 on the radially outward margin of thepressure plate engages the impeller shell thereby establishing amechanical torque flow path between the impeller and the turbine, theformer being connected to the crankshaft of an internal combustionengine. Pressure is distributed to the torus circuit through a flowpassage that is defined in part by ports formed in stationary statorsleeve shaft 138 that surrounds the turbine sleeve shaft 30. A similarflow path defined by the sleeve shaft arrangement for the converter isprovided for accommodating the flow of converter fluid from the toruscircuit, the flow path being shown schematically at 140 in FIG. 3.

The sleeve shaft arrangement defines also a central converter bypassclutch control pressure passage 142 which communicates through a radialport 143 in the turbine shaft 30 with clutch control chamber 146 formedbetween the clutch plate and damper assembly 126 and the adjacent wall122 of the impeller housing 120.

Control pressure passage 142 communicates with a bypass clutch controlvalve 144 which comprises a multiple land valve spool 145 and an alignedvalve plunger 148. Valve spring 150 urges the plunger 148 and themultiple land valve spool 145 in a left hand direction. That springforce is opposed by a pressure force acting on the end of land 152 ofmultiple land valve spool 145. Pressure is distributed to the valvechamber on the left side of the land 152 through a bypass clutchsolenoid pressure passage 154. As seen in FIG. 6, the solenoid windingswill actuate an armature push rod 207, which controls the seating forceof ball valve 209. That in turn controls the pressure in passage 154.

A bypass clutch feed pressure passage 156 communicates with controlvalve 144 at a location intermediate valve lands 158 and 160, the latterbeing smaller than the former so that a feedback pressure force opposesthe force of the spring 150. Bypass clutch control pressure passage 142communicates with the valve 144 at a location intermediate lands 158 and160. Land 158 controls the degree of communication between passage 156and exhaust port 162.

A pulse width modulated solenoid actuator and valve assembly is shown at164 in FIGS. 3 and 6. Solenoid feed pressure is distributed to theactuator and valve assembly 164 through a feed passage 166.

The solenoid valve driver is powered by battery 168. An electronicmicroprocessor, which will be described with reference to FIGS. 4A and4B, is shown in FIGS. 3 at 170. As will be described subsequently, theprocessor 170 receives input signals from various sensors which measureengine and vehicle operating conditions. The output of themicroprocessor is transferred through lead 171 to the bypass clutchpulse width modulated solenoid 164. The solenoid valve controlled by thepulse width modulated solenoid modulates the pressure in the solenoidfeed pressure passage 166 and delivers a control signal through line 154to the bypass clutch control valve. The clutch control valve iscalibrated to receive the control pressure of the solenoid output toestablish in line 142 and in control chamber 146 a pressure that willdetermine the controlled slip of the clutch.

FIG. 4A shows in schematic form the architecture of the processor 170 aswell as the relationship of the processor to the hydraulic control valvebody and to the transmission clutches and brakes. FIG. 4A shows theschematic arrangement of the various sensors with respect to theprocessor and the hydraulic control valve body.

The sensors, together with transducers not specifically illustrated inFIG. 4A, convert physical signals to electrical signals. Physicalsignals include throttle position or engine manifold pressure, enginespeed and transmission gear ratio selection as well as other variablessuch as engine temperature and the vehicle brake condition. Theprocessor inputs these signals and operates on them according to acontrol program or a strategy and then outputs the results to actuatorswhich function in cooperation with the hydraulic valve body to controlthe transmission. Processor 170 includes the central processing unit orCPU which comprises a computation unit and a control unit. An internalcontrol bus establishes a relationship between a memory unit and theprocessing unit. Other internal buses establish a relationship betweenthe CPU and the input conditioning signal circuit and the output drivercircuit.

The CPU executes programs that are fetched from memory and provide thetiming and controlled values of the output signals to the hydrauliccontrol valve body of the transmission. The input signal conditioningand the output driver system allow the microprocessor to read the inputdata from the microprocessor under the program control.

The memory portion of the processor 170 stores programs and data andprovides data to the processor as well as accepting new data from theprocessor for storage.

The memory portion of the processor 170 of FIG. 4A includes two types ofmemory; first, a read only memory or ROM which stores information ordata that is read by the processor in each background loop and, second,a random access memory or RAM which holds or temporarily stores theresults of the computations of the CPU as well as other data. Thecontents of the RAM can be erased, rewritten or changed depending uponthe operating conditions of the vehicle.

The two types of memory are stored in an integrated circuit in the formof a microprocessor chip whereas the computations performed by the CPUare the result of the function of a second integrated circuit comprisinga separate microprocessor chip, the two chips being connected by aninternal bus and interface circuitry.

One of the input signals to the processor 170 is a throttle positionsignal in line 172 which is received by a position sensor 174. An enginespeed sensor 176 in the form of a profile and ignition pickup (PIP)delivers an engine speed signal through line 178 to the processor 170.An engine coolant sensor 180 delivers an engine temperature signalthrough line 182 to the processor 170. A barometric pressure sensor 184delivers an altitude signal through line 186 to the processor 170.

A vehicle speed sensor 190 measures or senses the speed of the drivenelement of the transmission which is an indicator of the vehicle speed.That signal is delivered through line 192 to the processor 170.

The drive range for the transmission is selected by the vehicle operatorby manual adjustment of an adjustment lever schematically shown at 196.The various ranges are reverse, neutral, drive (D), direct drive ratio(3) and low speed ratio (1). Various shift patterns are established forthe three forward drive ranges D, 3, and 1, depending upon the positionthat is selected by the vehicle operator. The position that is selectedis sensed by the sensor and a position signal delivered through line 198to the microprocessor 170.

The microprocessor 170 includes also a subsystem identified asloss-of-signal-hardware (LOS). This hardware is adapted to establish anappropriate control signal for the output driver circuit that will causethe hydraulic valve body to continue operating with limited function inthe event of an electronic voltage failure in the system.

The electrohydraulic control valves, identified in FIG. 4B generally byreference character 200, include a valve body 202. The output signals ofthe processor 170 are delivered to the control valve body through aplurality of leads as shown at 204 through 210. Lead 204 (FIG. 5)carries a converter bypass signal which communicates with the PWMsolenoid 164, which communicates with valve 144. Valve 144 communicateswith passage 142 and chamber 146 as seen in FIG. 3. Lead 206 (FIG. 6)carries a control signal for a variable force solenoid pressure control.That signal depends upon throttle position, vehicle speed, torque, oiltemperature and altitude. Leads 208 and 210 carry shift solenoidpressure signals for effecting ratio changes in the transmission.

The output signals of the electrohydraulic controls 200 are distributedto the transaxle through control lines 216 through 226. Line 214corresponds to control passage 142 shown in FIG. 1. It extends to theconverter bypass clutch control chamber. Lines 216, 218, 220 and 222extends, respectively, to the forward clutch, the direct clutch, theintermediate clutch and the reverse clutch for the transaxle. Lines 224and 226 extend, respectively, to the overdrive brake band and to thelower and intermediate brake band for the transaxle.

The control system block diagram of FIG. 5 illustrates the overallsystem that is used to establish a so called clutch engage mode. Thedifferent operating modes, including the engage mode, will be describedsubsequently.

As seen in FIG. 5, the control logic 171 is embodied in the controlmodule or CPU of the processor 170. The various signals that arereceived by the processor 170 are illustrated. These correspond to thosedescribed with reference to FIG. 4A. As will be explained subsequently,the control logic 171 of the processor 170 calculates a target slip, orbetween actual engine speed and target engine speed and that value isrepresented by a signal in line 228. The control software andelectronics of FIG. 5 are incorporated into the control system.

For the purposes of this specification, the software for the electroniccontrol unit 170, exclusive of the peak-and-hold driver circuit 156,will be described in terms of hardware functions schematicallyillustrated in FIG. 5.

The system is effective to establish in the bypass clutch sufficientcapacity to hold the desired slip at the current torque. Torquetransients then are absorbed by momentary periods of increased slip asthe controller establishes a new output signal for the solenoidcorresponding to the new torque condition.

Numeral 230 designates the internal combustion engine, and numeral 232designates an engine speed sensor which measures crankshaft speed. Thetransaxle or transmission has a turbine speed sensor 234. The outputsignal of the turbine speed sensor 234 is sampled via signal flowcontrol path 236 and input sampling switch 238 to the control logic 171of the processor 170. The turbine speed signal is sampled also by acomparator register 240.

Engine speed measured by the sensor 232 is sampled via signal flow path242 and input sampling switch 244 by the control logic of processor 170.The signal is sampled also by the comparator register 240.

The comparison at the register 240 determines whether there is anydifference between the turbine speed and the engine speed. This value iscalled actual slip, and the value of that actual slip is represented bya signal in lead 246 which is distributed to summing point 248. Thedifference between the value of the signal in lead 246 and the targetsignal in lead 228 is measured at summing point 248 to establish anderror signal in line 250. This error signal is distributed to aproportional-integral-derivative controller logic portion of theprocessor 170. PID controller is shown at 252. This controller may be ofa well known variety. It is inserted into the control loop to form apart of the forward gain of the control system. It effects proportionalcontrol, an integral control and a differential control. By adjustingthe magnitude of these terms, the actual signal that is the output ofthe PID controller can be modified so as to produce the required systemresponse.

The proportional control feature of the PID controller makes it possiblefor the output of the controller to be varied directly with the errorsignal. It produces a so called gain factor, which is a measure of thecontrol gain in the system that reduces accordingly the magnitude of anycurrent errors. Because the proportional control by itself, ofnecessity, establishes a gain factor of limited range, it is notsufficient to achieve the desired response due to steady state errors orundesired slip oscillations. The integral control component of the PIDcontroller eliminates steady state error for improved system accuracy.The response can further be improved to effect system stability andeffective transient response of the system by introducing the derivativecontrol. This introduces a stabilizing effect on the system because ofthe addition of phase lead to the control loop.

The output of the PID controller is a duty cycle signal that followssignal path 254. This is received by a peak-and-hold driver circuit 266for the pulse width modulated solenoid 164, the latter being connectedto the driver circuit 266 through line 204.

Although we have described in this specification a PWM solenoid, it iscontemplated that the system could be adapted to use instead a variableforce solenoid (VFS).

The peak-and-hold circuit for the PWM solenoid may be of a conventionaltype. It is effective to establish at the input side of the solenoid adriver voltage similar to that shown in FIG. 12 upon receipt of a signalfrom the PID controller. As shown in FIG. 13 at 260, the peak- and-holdcircuit establishes a change in the solenoid input represented by thesteep slope portion 262 of the curve in FIG. 12. During the initial partof the hold time during which the controller output voltage isestablished at a value shown at 264, a peak current is established bythe driver as shown at 266. This overcomes the initial friction andinertia of the solenoid (pull-in). That event is followed by a moderatehold current value as shown at 264 until the termination of the dutycycle on-time at 270. The cycle is repeated again in the next duty cycleperiod.

The output of the solenoid valve 258, which would correspond to thesolenoid valve 164 of FIG. 3, is distributed to the bypass clutchcontrol valve 144 described with reference to FIG. 3. The output of thebypass clutch control valve is a pressure signal in passage 142 which,as explained with reference to FIG. 3, communicates with controlpressure chamber 146 for the converter bypass clutch 126.

The hydraulic valve body 202 includes a throttle valve assembly asdescribed in the references identified in the background art discussion.The throttle valve assembly establishes a pressure signal as anindicator of engine torque and other variables as explained above. Thethrottle valve is identified by reference numeral 260 in FIG. 4B. Theoutput of the throttle valve assembly supplies the desired pressure tothe valve body 202. A transmission oil temperature sensor shown at 262distributes a signal through line 264 to the input signal conditioningportion of the microprocessor 170, as shown in FIG. 4A.

FIG. 7 shows the shift schedule information that is stored in the ROMportion of the memory for the microprocessor 170. As indicated, forevery vehicle speed, there is a throttle opening at which a ratio changewill occur. Each ratio change, regardless of whether it is an upshift ora downshift, has its own shift point schedule as indicated in FIG. 7.For example, for a 60° throttle opening, a 2-1 downshift will occur atapproximately 15 miles per hour and a 1-2 upshift will occur atapproximately 22 miles per hour. Microprocessor 170 will initiate theshift command signals in response to the information provided by theinput sensors. It initiates also the lockup clutch engagement andrelease signals.

The behavior of the lockup clutch during a shift interval now will bedescribed with reference to FIGS. 8, 9, 10 and 11.

Shown in FIG. 9 is the relationship between time, plotted on theabscissa, and engine turbine speed and a dimensionless characteristicidentified as percent shift complete plotted on the ordinate. Thisrelationship of FIG. 9 occurs following a shift command and continues tothe time that the shift is complete. Prior to the initiation of theshift command, the characteristics of the converter are determined bythe PID controller described with reference to FIG. 5. This PID controlis similar to the PID control during steady state operation described inthe previously identified copending patent application.

As indicated in FIG. 9, the processor will command a shift at a timeshown at 270 in FIG. 9. When the clutch is in steady state operation,before a command for the shift is made at 270, the engine speed shown at272 and the turbine speed shown at 274 are generally parallel, whichindicates that the target slip has been achieved. The magnitude of theslip indicated as a steady state slip in FIG. 9 is the difference at anytime between the engine speed, sensed by the processor, and the turbinespeed sensed by the processor. The turbine speed and the engine speedare measured once each background loop as time progresses on thehorizontal axis.

As indicated in the copending patent application identified above, thedesired slip is set equal to the actual slip at the time that engagementof the bypass clutch is commanded. The desired slip then is decayed orramped downwardly toward a target value at a rate that is calibrateduniquely for each gear ratio. The desired slip is calculated during eachbackground loop. The decayed or ramped desired slip value is compared tothe actual slip to detect an error. Duty cycle for the bypass clutchsolenoid control valve is determined so that the actual slip decaystoward a target value until it reaches the target slip. This control ofthe clutch during the steady state operating mode will be referred tohereafter as the PID control mode.

As mentioned earlier, a shift occurs at time 270, shown in FIG. 9, forthe controller for the present invention. At time 270, an upshift, forexample, is commanded to occur between a third ratio and a fourth ratio.A calibration constant, which is a dimensionless value PCUPSCMPT, isplotted in FIG. 9. The various constants, one for each shift, arebetween the value 0 and the value 1, as indicated. The constant that isretrieved by the controller will be dependent upon the shift beingexecuted. Immediately the target engine speed then will change from avalue at 276 to a value at 278.

The actual engine speed, which is plotted as shown at 280, begins torise. The desired slip, as shown by the dotted line 282, is not allowedby the processor to proceed immediately to the slip value correspondingto the target engine speed 278 because that would exceed the controlcapacity of the processor. Instead a maximum rate is fetched from theROM register where a maximum rate for the 3-4 upshift is stored, andthat rate value is multiplied by the engine speed value at 276 toproduce the slope indicated by the desired slip line 282. Finally, thedesired slip line will blend with the target engine speed line asindicated at 284.

As the routine continues following the command of the shift, the errorbetween the engine speed line 280 and the desired slip line iscontinuously monitored. That error is used to calculate a duty cycle forthe bypass clutch solenoid control valve in a manner described inpreviously mentioned U.S. Pat. No. 5,029,087 as well as in the copendingpatent application identified above.

At 286, the turbine speed, which is continuously monitored by theturbine speed sensor, begins to slope downward as does the engine speedafter the engine speed reaches a peak as shown at 288. At the time theturbine speed begins to ramp downward, the percent complete that iscalibrated and stored in RAM begins to rise as indicated at 290. Thatpercent complete value is constantly being computed by themicroprocessor. One computation is carried out each background loop. Themicroprocessor determines the value for percent shift complete using theequation:

TRANSMISSION RATIO MINUS OLD GEAR RATIO/GEAR RATIO CORRESPONDING TO ACOMPLETED 3-4 UPSHIFT MINUS THE GEAR RATIO FOR THE BEGINNING OF THEUPSHIFT, NAMELY, THIRD RATIO.

The transmission ratio is equal to the turbine speed divided by theoutput shaft speed. The gear ratio at the beginning of the upshift is acalibration parameter fetched from memory and the gear ratio at the endof the upshift also is a calibration parameter stored in memory. In thisequation, the turbine speed is the only variable, assuming the vehiclespeed during the shift interval does not change or changes only anegligible amount. The others terms are calibration constants. Thus, asthe turbine speed changes, as indicated in the graph of FIG. 9, thepercent shift complete value begins to rise as shown at 290.

At a percent shift complete value of about 85%, which is a value "x"(see FIG. 9) chosen by the transmission calibrator, the shift isconsidered to have been completed. That percentage is indicated at 292in FIG. 9. Between the point 294 and the point at 292 where the shift isconsidered to have been completed, the turbine speed falls and theactual slip is continuously monitored. The error is the differencebetween the actual engine speed and the target engine speed value. At atime later than the time indicated at 296, the actual engine speed isfor all practical purposes equal to the target engine speed.

A target engine speed is determined using the function illustratedgraphically in FIG. 10 where the percent shift complete value is plottedon the horizontal axis and the target slip value, measured in rpm, isplotted on the vertical axis. The relationship is indicated by thesloped line 298. Point 300 corresponds to point 294 in FIG. 9 where thepercent shift complete value begins to change. Beginning at point 300 inFIG. 10, the target slip value decreases until point 302 is reached, atwhich time the shift is approximately 85% complete.

As will be explained subsequently, the target slip value will continueto be determined as shown at 304 from the shift control function of FIG.10 until a post-shift timer expires or until a zero target slip isreached at the 100% complete shift point 306.

The curve representing target engine speed increases as shown at 284 andthen slopes downwardly as duty cycle changes along a negative slope line308 after having reached a peak at 310. This line represents the enginespeed that is needed in order to achieve the target slip value shown at298 in FIG. 10. As previously mentioned, this line is a calibratedfunction stored in memory.

After the percent complete value corresponding to 85% shift completionis reached, the routine will continue at a post shift control phasecausing continued clutch control until the post-shift timer expires. Atthat time the percent shift complete value changes along line 310 inFIG. 9. A transition then may be made to the so-called hard lock mode asdescribed in the copending application identified above.

Shown in FIG. 8 is a plot of time versus slip, which indicates a steppedvalue for the target slip. A calibration constant will determine thetarget slip value during steady-state operation as shown at 312 in FIG.8. At time 314, for example, a shift command may be issued by theprocessor to change the ratio from the third ratio to the fourth ratio.The processor will not immediately respond by supplying a target valueof zero slip. Rather, an intermediate target value of perhaps 400 RPMwill be fetched from memory. The target value depends upon the ratiosthat are involved in the shift as well as the throttle position andvehicle speed. As indicated earlier, however, the processor will notimmediately respond to produce an intermediate target value of 400 RPM.Rather, it will produce a ramped desired slip curve 316 by multiplyingthe steady-state target slip, which is equivalent to the actual slip atpoint 318 by a maximum rate which is the calibrated value obtained frommemory at the instant the shift is commanded at 314. Thus, the desiredslip will vary as indicated by the ramped line 316 until it reaches theintermediate target slip value of 400 RPM.

In actual practice, the steps between 1020 RPM, indicated in FIG. 8, andthe intermediate level of 400 RPM occurs in several ramped steps ratherthan a step of 600 RPM. Typically, the maximum RPM difference that ispermitted by the processor is about 50 RPM per background loop.

After the steady-state condition at point 320 is reached, the processorwill command again a further increment until a lower target value isreached. The lower target slip value is indicated in FIG. 8 at 322. Thismay represent a slip of about correspond, for example, to the slip thatis detected at the completion of the shift as shown at point 324.Following completion of the shift, a PID control will occur in the samefashion as described previously to produce a ramped desired slip value326 corresponding to ramped desired slip curve 316 and ramped desiredslip curve 328, which appears intermediate the target values 400 RPM and50 RPM. As the desired slip is ramped downward as shown at 326, thetarget value will slope downward at shown at 328 until the 100% shiftcompletion point 330 is reached. This represents a transition to theso-called hard lock operating mode, which is described in the copendingapplication identified above.

As seen in the graph of FIG. 10, every shift will have a uniquefunction; that is, there will be a separate function for a 3-4 upshift,a 4-3 downshift, etc. There will be a separate shift complete constantas well for every target which is computed every background pass. Thevalues for target engine speed in FIG. 9 are those speeds that areneeded to achieve that target each background pass.

In FIG. 11, we have shown in the form of a software flow chart the stepsinvolved in controlling the bypass clutch during a shift interval. Eachof the software steps represents an event that occurs only one time inthe background loop of the processor after the event is commanded forthe first time.

The process begins at step 310, where an inquiry is made as to whether ashift has been commanded during the current background pass. If it hasbeen commanded as shown at 270 in FIG. 9, the value for the current slipis measured in a "snapshot" fashion, and that value for slip is storedin temporary storage registry in the RAM portion of the memory. Thatvalue is used, as discussed previously with reference to FIG. 10, tocalculate a target engine speed. The calculated engine speed is equal tothe turbine speed at the start of the shift plus the target slip valueindicated in FIG. 10, which is a function of the percent of shiftcomplete value.

The current slip is observed at action block 312. At the same time, thetimer is started at action block 312. Thus Timer 1 = Time 1.

The slip is calculated after the slip value is stored and the timer isstarted at action block 312 as the routine proceeds to action block 314.If the inquiry at step 310 is negative (i.e., if the shift has not beencommanded), an inquiry then is made at step 316 as to whether a shiftcurrently is in progress. A positive response then will result inadvancement of the routine to step 314 as indicated above. A negativeresponse at step 316 would indicate that the shift has reached the 85%complete point. An inquiry then is made at step 318 to determine whetherthe post shift control is in progress. If the post shift control is inprogress, the routine then will proceed back to step 314 as indicated,where the slip is calibrated in the manner previously described toproduce the ramp shown at 326 in FIG. 8. If a post shift control is notin progress, that indicates that the post shift control is completed andthe routine then will proceed to establish a zero slip condition, or aslip condition near zero starting with action block 320, which will bedescribed subsequently.

After the operation at action block 314 is completed, a check is made ataction block 322 as to whether the shift has been completed during thecurrent background pass. This is done by comparing the results of thecomputation of the percent shift complete value described above to apredetermined value, such as 85%. If the shift complete value is lessthan 85%, that indicates that the shift has not yet been completedduring the current background pass and the response to the inquiry at322 would be negative. On the other hand, if the shift complete valueequals at least 85%, the response is positive and a timer is set at step324. This timer can be the same timer that was used at action block 312to establish a time limit for achieving a shift beginning with the shiftcommand and ending with the 85% shift complete point. Since there is nofurther need for timing that event, the same timer can be used now for adifferent purpose and it is reloaded with a new time fetched from memoryfor establishing a time before which the shift must be completed betweenthe 85% shift complete point and the point at which the final targetvalue of zero percent, or a near zero percent value, is reached.

The slip tables used by the processor can have values of between 0 and1020 RPM with 4 RPM resolution. A slip greater than 1020 RPM can becommanded by setting the maximum attainable slip target value in RPMgreater than 1020. The final value of target slip, of course, determinesthe control mode. A target slip of between 0 and 4 RPM is normallyconsidered to be a hard lock mode. A slip target value of between 4 and500 RPM normally is considered to be an engaged mode. The target slipduring the engage mode is achieved in a closed loop manner using the PIDcontroller described above with reference to FIG. 5. The shiftmodulation logic described with reference to FIGS. 9, 10 and 11 controlsthe length of time after a shift is commanded that additional bypassclutch modulation occurs to effect a transient increase in slip untilthe shift is completed.

The routine then will proceed to step 328 where the maximum rate for theslip change is obtained from memory. That value is a function thatdepends upon the shift that is in place. The function being differentfor each ratio change, regardless of whether it is an upshift or adownshift. It is this value that determines the slope of the desiredslip shown at 326 in FIG. 8. This is an event that follows theachievement of the 85% shift complete point 324. This establishes amaximum allowable rate of change; that is, the maximum rate that isallowed regardless of the target value that is specified. The actualdesired slip that is detected by the PID controller for control purposesis the value indicated by the line 328 in FIG. 8. This value is input tothe comparator 248 in FIG. 5 on the signal flow path 228 of FIG. 5.

The routine then proceeds to step 330 where the maximum RPM increment isdetermined as the slip approaches the desired slip. As indicated earlierwith reference to FIG. 8. The controller will not allow a full RPMchange from the present target value to a zero value in a single step. Amaximum increment is established so that the target slip will change insteps as indicated in FIG. 8 until the zero target value is reached. Atstep 330, that maximum rate is multiplied by the background time for oneloop of the processor. Having determined the maximum RPM increment atstep 330, the routine then will proceed to step 332 where that incrementis compared to the calculated slip. If the calculated slip is greaterthan the increment, the controlled slip will be allowed to change by theamount of that increment at step 334. This corresponds to the step from400 RPM to 50 RPM in the graph of FIG. 8. On the other hand, if thedifference between the calculated slip and the controlled slip is notgreater than the increment determined at step 330, then the routine willbe bypassed to step 336 where the controlled slip is set equal to thecalculated slip. Thus, the controlled slip is allowed to reach a minimumvalue, and this is done in accordance with the PID control procedurepreviously described. This procedure occurs at step 338. The result ofthat procedure is a slip slope line of the kind shown at 328 in FIG. 8.In FIG. 8, the control slip is zero, but the actual slip could be chosento be greater than zero; for example, 4 RPM.

The procedure indicated at steps 330 through 338 occurs during shiftingand the processor will continue to proceed through these stepscontinuously, even after the shift has been completed.

In a post shift control procedure, which begins at 320. The process flowchart for the post shift control will terminate at step 320. Theprocedure previously described with reference to the shift control logicthen will be carried out in the same fashion described previously.

The post shift control logic begins at step 320 as mentioned earlier.The target slip value indicated in step 320 usually is zero, but itcould be some value other than zero. Target slip is set to some tablevalue which depends upon throttle position and vehicle speed asdescribed earlier, and is obtained using a table look-up.

The routine in the post shift control process then will proceed to step340, where an inquiry is made as to whether the post shift control isover for the first time in the current background pass. If the postshift control is over, a transition will be made to the steady-statemode as the controlled slip is ramped down to the final target value. Ifthe inquiry at step 340 is positive, a timer is set at 342. A separatetime is set for the completion of the post shift control, depending uponthe gear ratios that are involved in the shift. A check then is made atstep 344 to determine whether the timer that is set at step 342 hasexpired. A negative response to the inquiry at step 340 will result inthe routine proceeding directly to the timer check at step 344. If thetimer has not expired, the post shift control then can continue. The maxrate that is fetched from memory is set at step 346. This is similar tothe max rate function described with reference to step 328. As in thecase of the shift in progress procedure described above, every shift inthe post shift control has a different rate depending upon the ratiosthat are involved in the ratio change.

If the inquiry at 344 is negative, that means the timer has run down. Asindicated in FIG. 11, the flow diagram designates a non-shiftingcondition. The step 348 then determines a max rate of change of slip forthe higher gear ratio in the upshift and the flow diagram then proceedsto step 330 where the routine passes through the previously describedsteps 330 through 338 to the exit.

Having described a preferred embodiment of the invention, what isclaimed is:
 1. An automatic transmission for use in an automotivevehicle driveline for delivering torque from a throttle controlledengine to vehicle traction wheels comprising:multiple ratio gearingestablishing plural torque flow paths from said engine to said tractionwheels and a hydrokinetic unit having an impeller connected to saidengine and a turbine adapted to be connected to torque input elements ofsaid gearing; a fluid pressure operated friction bypass clutch situatedin said hydrokinetic unit adapted to selectively connect said impellerand said turbine to establish a mechanical torque bypass flow patharound said hydrokinetic unit; clutch means and brake means forcontrolling gear ratio changes; said bypass clutch having a clutchcapacity control chamber which, when pressurized, determines the torquetransmitting capacity of said bypass clutch; a control valve circuitincluding a fluid pressure source and shift valve means communicatingwith said clutch means and said brake means and with said pressuresource; bypass clutch control valve means for effecting controlledpressure distribution to said clutch capacity control chamber; shiftsolenoid valve means for selectively actuating said shift valve meansfor effecting gear ratio changes; vehicle speed sensor means fordeveloping a vehicle speed signal; turbine speed sensor means fordeveloping a turbine speed signal; engine throttle position sensor meansfor developing a throttle position signal; engine speed sensor means fordeveloping an engine speed signal; and electronic processor means forreceiving said signals and for controlling operation of said shiftsolenoid valve means and said bypass clutch control valve means; saidprocessor means including means for modifying operation of said bypassclutch control valve means to effect a reduced bypass clutch capacityfollowing a command of a ratio shift until said shift is completed; saidmodifying means including means for developing a controlled increase inbypass clutch capacity following an initial bypass clutch capacitydecrease during a shift, the amount of said controlled increase beingfunctionally related to the percent of completion of said shift.
 2. Anautomotive vehicle driveline having a throttle controlled internalcombustion engine and a multiple ratio transmission, said transmissionhaving gearing and a hydrokinetic torque converter with an impellerconnected drivably to said engine and a turbine connected to torqueinput elements of said gearing;a torque converter bypass clutch meansfor establishing a frictional driving connection between said impellerand said turbine; a transmission control including means for effectingautomatic ratio changes in said transmission during a shift interval inresponse to vehicle speed and engine throttle position changes; andmeans for modifying the torque transmitting capacity of said bypassclutch means following the initiation of a ratio change and forsubsequently effecting an increase in said torque transmitting capacityduring said shift interval, modification of said capacity by saidcapacity modifying means being functionally related at each instantduring said shift interval to the percent of shift completion wherebyshift smoothness results from the resulting reduction in rotary inertiaforces in said driveline.